Historically, the greatest damage to domestic animals and crops has been caused and continues to be caused by pests such as insects, fungi, nematodes and microbes. Insects particularly represent a cause for concern as they are the most numerous of all living organisms and constitute approximately 72% of all animal species. Approximately 1% of insects are considered pests in that they attack humans and/or domestic animals, transmit human, animal and plant diseases, destroy crops, objects and structures and compete for food and other necessities. It is estimated that enormous agricultural losses result worldwide from insect presence.
Domestic animals which include animals of agricultural worth such as sheep, cattle, horses, goats, pigs and other ruminants and monogastrics are almost invariably subject to the activity of pests including insects, acarides, acarina, siphonaptera, phthiraptera, anoplura and mallophaga. External parasites such as ticks, lice and fleas irritate the animals and can cause economic loss in the form of poor quality hide, wool or sheep skin, poor quality meat/tissue, reduced weight gain and even death as a result of the animal carrying harmful parasites.
The losses resulting from insect caused human and animal diseases are also enormous. In fact, insects are considered to be the carriers of more than 250 viruses which are pathogens of humans and higher animals. The numbers of human deaths caused by mosquito transmitted diseases such as malaria and lymphatic filariasis are huge. Flies also transmit human and animal related diseases such as trachoma, trypanosomiasis and river blindness.
However, out of the nearly one million species of arthropods which includes lice, ticks, flies and mites, only a small percentage require the application of control measures. To date, the primary method for controlling insects and other pests, particularly in respect of domestic animals (such as sheep, cattle, goats, horses and hogs) has been by the application of synthetic chemical pesticide compositions. It is estimated that there are at least 35,000 formulated pesticide products worldwide with chemicals as the active ingredients. Such pesticide products include antimicrobials, larvicides, insecticides, animal dips, avicides and disinfectants.
The extensive use of chemical insecticides since the 1940s has resulted in a large number of problems including widespread insect resistance, emergence of secondary pests, hazards to human and animal health as well as detrimental effects on fish and birds, environmental pollution and the increasing economic costs of new insecticides.
Many insect species have developed resistance to the action of specific insecticides so as to necessitate changes in control practices. There is an ever-widening pool of insect pests which are developing multiple resistance. The resistance genes having lengthy persistence in insect genomes which preclude successful reuse of an insecticide to control an insect population with resistant genes.
Pesticide/insecticide residues and their consequential many potential human, animal and environmental risks are also seen as one of the major problems resulting from chemical usage, particularly those formulations containing active agents which include organophosphates or synthetic pyrethroids. With the exception of microbial insecticides, nearly all pesticides result in residues of various chemicals and their degradation products or metabolites which may be present in detectable amounts (ppb to ppm) in food despite food processing. Tissue/meat residues are also a major concern when considering use of insecticides on farm animals.
Potential human risks from the use of such insecticides include acute toxic reactions to the insecticide such as poisoning, skin and eye irritations, as well as possible long term effects such as cancer, birth defects, and reproductive disorders. Acute inhalation toxicity as well as dermal penetration are also potential risks. Health hazards in humans may also arise from repeated exposure to a chemical over a limited period of time.
In particular, the currently used actives of synthetic pyrethroids and organophosphates which are commonly used in insecticidal formulations to control lice and flies, particularly on sheep, are not only toxic to animals but also to the human operator who applies them. Exposure in farmers or operators who handle both pesticide concentrates and the larger volumes of pesticide diluted for use, is a cause for concern. Further, it is possible for the operator to ingest pesticides not only by mouth, but also by breathing (eg spray drift) and by absorption through the skin (accidental spillage). Of particular concern has been the use of organophosphates where accidental exposure causes acute and chronic poisoning affecting the nervous system.
Accordingly, insect and other pest control has been sought to be directed away from exclusive reliance on insecticides and towards the optimisation of environmental and economic insect and pest control (integrated pest management). The application of microbial control in which insects are attacked by pathogens such as viruses, bacteria, fungi and protozoa are favoured as such microbial insecticides are highly selective for insect pests and do not leave toxic residues. However, such microbial insecticides are not without their problems such as the difficulty in applying as well as confining the natural enemy/parasite/disease to a large area. Further, they also have the disadvantage of short residual action and extreme specificity which limits general applicability.
Biological control has been recently applied in the area of insecticides/pesticides through the release of sterilised male insects. Genetic engineering has also recently been applied by way of mass introduction of deleterious mutations such as chromosomal translocations. However, such procedures are very expensive and stringent criteria are required before release of sterile males is contemplated. Chemosterilants which sterilise large segments of insect pest populations are also known but are strong carcinogens which precludes their use.
The use of chemical insecticides and pesticides and their environmental and economic viability, the dangerous nature and magnitude of the persisting residues as well as increasing insect and pest resistance, together with high toxicity levels of many chemical insecticides, has resulted in the search for new substances or approaches to insect and other pest control.
There is therefore a need for compounds and combinations thereof which can be used as active agents in pesticides, particularly against insects which afflict domestic animals or their environs, and which are effective at low application rates, selective in biologic action and have low toxicity and a high margin of safety to humans, crops, economic animals, aquatic organisms and birds. Such compounds and combinations must be both environmentally friendly in that there must be demonstrably low impacts on the environment, as well as economically viable to use on a large scale. Further, there must be none or little insect or other pest resistance to such compounds or combinations. Fermentation product A83543, also known as spinosyn, includes a family of related compounds (spinosyns) produced by Saccharopolyspora spinosa. These are naturally derived fermentation products with a positive safety profile in contrast to currently used synthetic organically derived compounds (such as synthetic pyrethroids, organophosphates, organochlorines and carbamates), and have previously been shown to exhibit excellent insecticidal activity. Accordingly by the term “A83543 compounds” which has the same scope as the phrase “spinosyn and derivatives and analogues thereof” is meant components consisting of a 5,6,5-tricyclic ring system, fused to a 12-membered macrocyclic lactone, a neutral sugar (2N,3N,4N-tri-O-methylrhamnose) and an amino sugar (forosamine). The family of natural components of A83543 include a genus taught in EPO patent application No. 0375316 and having the following general formula:
wherein R1 is H or a group selected from
and R2, R4, R3, R5 and R6 are hydrogen or methyl; or an acid addition salt thereof when R1 is other than hydrogen.
The family of compounds from A83543 fermentation product has been shown to comprise individual compounds A83543A, A83453B, A83543C, A83453D, A83543E, A83453F, A83543G, A83453H, A83543J, A83453L, A83543M, A83453N, A83543Q, A83453R, A83543S, A83453T, A83453U, A83543V, A83453W, A83453X. Boeck et al. described spinosyns A-H and J and salts thereof in U.S. Pat. Nos. 5,362,634, 5,496,932 and 5,571,901 which are incorporated herein by reference. Mynderse et al. described spinosyns L-N, their N-demethyl derivatives and salts thereof in U.S. Pat. No. 5,202,242 incorporated herein by reference. Turner et al. described spinosyns Q-T, their N-demethyl derivatives and salts thereof in U.S. Pat. Nos. 5,591,606, 5,631,155 and 5,767,253 which are also incorporated herein by reference. Spinosyns K,O,P,U,V,W, and Y are described in the article by DeAmicis, C. V. et al. in American Chemical Society's Symposium Series: Phytochemicals for Pest Control (1997), Chapter 11 “Physical and Biological Properties of Spinosyns: Novel Macrolide Pest-Control Agents from Fermentation” pp 146-154.
Spinosyn A (A83543A) was the first spinosyn isolated and identified from the fermentation broth of Saccharapolyspora spinosa. Subsequent examination of the fermentation broth revealed that the parent strain of S. spinosa produced a number of spinosyns (A83543A to J). Compared to spinosyn A, spinosyns B to J are characterised by differences in the substitution patterns on the amino group of the forosamine, at selected sites on the ring system and on the neutral sugar. The strains of S. spinosa produce a mixture of spinosyns which primary components are spinosyn A (˜85%) and spinosyn D (˜15%). These are the two spinosyns that are currently known as the most active as insecticides.
Similar to the spinosyns, macrocyclic lactones have also previously been shown to exhibit excellent insecticidal activity. Macrocyclic lactones have a complex ring structure and include such well known anthelmintic compounds as avermectins and milbemycins. The avermectins are isolated from fermentation products of Streptomyces avermitilis and ivermectin is a compound which is a semisynthetic chemical formed by modification of avermectin. The basic structure of the avermectins is a 16-membered lactone ring to which are appended three main substituent groups: a hexahydrobenzofuran group, a disaccharide group (at C-13) and a spiroketal ring (C-17 to C-28). Doramectin is a novel avermectin. Milbemycins are other compounds which are not avermectins but which can be considered to come within the class of compounds which are macrocyclic lactones. The milbemycins differ structurally from the avermectin group, mainly in the absence of a disaccharide group on C-13. Milbemycin D and milbemycin 5-oxime are two such macrocyclic lactones. Moxidectin is derived from the fermentation product nemadectin and possesses a methoxime substituent on C-23.
The present invention resides in the discovery of a synergistic combination of pesticidal compounds, the formulation and application of specific pesticidally active agents based on the synergistic combination and their use in pesticidal formulations against Phthiraptera, Siphonaptera and Acarina pests, particularly in domestic animals.